1. From the Department of Internal Medicine, Division of Nephrology (J.L.F.-G., D.G., S.J.L.B.), University of Groningen, University Medical Center Groningen, the Netherlands
2. Laboratory Corporation of America Holdings (LabCorp), Morrisville, NC (M.A.C., J.D.O.).
3. Department of Internal Medicine, Division of Endocrinology (R.P.F.D.), University of Groningen, University Medical Center Groningen, the Netherlands